This invention relates to a master fluid power cylinder capable of performing useful work while simultaneously controlling the coordinated operation of an associated slave cylinder or cylinders which also perform useful work. In such combinations, it is often required that the pistons and the rods of the two cylinders start their movement at the same time, travel at substantially the same velocity, and reach the ends of their respective strokes at substantially the same time. This is necessary, for example, when two such cylinders are used to raise and lower opposite ends of the reel on a combine. Uniform movement, if desired, is achieved by sizing the master and slave cylinders so the rod end volume of the master is equal to the head end volume of the slave cylinder or cylinders. It should be understood that this alternatively can be accomplished by using the same size cylinders and designing the associated mechanical linkages to accommodate the differing strokes.
It also should be understood that this invention is applicable to systems having a master cylinder and any number of slave cylinders in a series mode. In such systems a single re-phasing valve would be required at either end of the cylinder as determined by use preference and the master cylinder and all slave cylinders typically would be double acting cylinders, such as shown in my application Ser. No. 830,713 filed Sept. 6, 1977 and entitled "Plow System".
However, wear of the working parts, particularly the fluid seal, cause the cylinders to get out of synchronization. That is, when hydraulic fluid within the system leaks out or leaks around seals from one section of the system to another, the predetermined relationship between the piston and rod and master cylinders will be disturbed. When this occurs the cylinders are said to be out of phase and the operation for correcting this condition is called "re-phasing". Mechanisms for automatically re-phasing hydraulic cylinders are disclosed in U.S. Pat. No. 3,347,043 issued to E. G. Freese and U.S. Pat. No. 3,832,852 issued to L. W. Schmucker. The device of the former patent restricts the location of the fitting on the cylinder (precluding a design in which the fittings are located on the ends of the cylinder, for example), requires precise location of the fitting relative to the port and orifice in the cylinder wall and tends to weaken the cylinder wall by placing the large port in close proximity to the orifice. In addition if the master cylinder is not provided with wear rings, a load transverse to the axis of the piston rod acting on the outer end of the piston rod will deform the seal bringing the piston into metal to metal contact with the cylinder wall in the vicinity of the orifice. When this occurs, the re-phasing function will be defeated, requiring either the use of more expensive wear rings in the piston of the master cylinder or relocation of the fittings around the periphery of the cylinder. The use of slots or grooves on the interior of the cylinder wall, as suggested by the latter of the aforementioned patents, also has a slight tendency to weaken the cylinder wall, but more importantly necessitates flow of the fluid necessary for rephasing past the piston seal per se. Even though the time duration during which flow takes place is relatively small, repeated cycling of the cylinder subjects the seal to a higher potential for erosion damage.
It is therefore an object of this invention to provide a master cylinder construction which is relatively strong, which permits the use of normal standard fittings positioned most expeditiously for fluid flow ingress to and egress from the cylinder and which provides good life for the seal of the master cylinder piston. It is also an object of this invention to provide a master cylinder construction in which the means for re-phasing can be positioned around the periphery of the master cylinder to minimize the adverse effects of external forces on the cylinder rod.